PRTN3 and rheumatoid arthritis: In the present study, we have used one single method, proteomic-type LC-MS/MS [28], to simultaneously investigate differences both in the protein/peptide abundances and in IgG1–4-Fc glycan structures in ACPA-IgG and in non-ACPA-IgG derived from serum/plasma and synovial fluid samples from ACPA positive RA patients.